First-principle study of the influence of hydroxyapatite on magnesium surfaces

TL;DR

This study uses density functional theory to analyze how hydroxyapatite coatings and doping elements like calcium and zinc affect magnesium surfaces, providing insights for biodegradable implant surface design.

Contribution

It offers the first detailed atomic-level understanding of HA adsorption on doped Mg surfaces, highlighting the effects of dopants on surface interactions and electronic structure.

Findings

Zn and Ca doping improve HA adsorption on Mg surfaces

Dopants cause surface deformation and atomic rearrangements

Ca dopant can migrate into HA layer, creating Mg vacancies

Abstract

Hydroxyapatite (HA) on a magnesium (Mg) surface is studied using density functional theory, to help understand the effect of HA coating and alloying in the surfaces of Mg-based biodegradable implants. We determine the adsorption energies and structural changes of a single layer of HA on pure Mg(0001) and on sparsely calcium (Ca) or zinc (Zn) doped Mg(0001) and find that both Zn and Ca doping improves the adsorption, except in a few positions of HA relative to the dopant position. All adsorption configurations, whether with pure or doped Mg surfaces, show deformation of the surface and HA layer. For Ca doping, we found that for a certain adsorption configuration, the dopant Ca atom moves out of the Mg surface and into the HA layer, leaving behind a Mg vacancy in the top layer of the Mg surface. Plots of electron density changes show that electrons accumulate around the Ca dopant and the neighboring Mg atoms, while in Zn doping this is less pronounced. Overall, our results demonstrate that the dopant choice and relative position of HA influence the interaction between HA and Mg-surfaces, and affect both adsorption energies and atomic and electronic structures.